1. Field of the Invention
The present invention relates to a device manipulation interface technique of measuring an electroencephalogram of a user and, based on the measured electroencephalogram, enabling control of a device as desired by the user. More specifically, the present invention relates to a device manipulation interface technique for being incorporated in a wearable device such as a head-mount display (HMD) to make it possible to select and activate a function of the wearable device or another device on the basis of an electroencephalogram of a user.
2. Description of the Related Art
In recent years, wearable devices such as head-mount displays (HMD) are gaining prevalence due to decreases in the size and weight of devices. As interfaces of many devices, hardware-based methods are in use, e.g., pressing a button, moving a cursor to make a decision, and manipulating a mouse while looking at a screen. However, if the aforementioned physical manipulations are required when controlling a device whose main body has a small size and which is characterized to be handsfree, e.g., an HMD, the handsfree feature will be undermined, thus being ineffective. Therefore, attention is drawn to interfaces for controlling a device without performing any physical manipulations, specifically, easy-to-use interfaces utilizing an electroencephalogram that make it possible to control a device by merely thinking.
An electroencephalogram is an encephalic activity (electrical activity of cranial nerve cells) measured as an electrical signal based on a difference in potential between a reference electrode and an measurement electrode. An example of an interface utilizing an electroencephalogram is a method and apparatus of determining a human psychological state and the like by utilizing an event-related potential which is described in Japanese Laid-Open Patent Publication No. 2005-34620 (herein after “Patent Document 1”).
Patent Document 1 discloses a technique of determining an option which a user wishes to select by utilizing a characteristic signal of an event-related potential of his or her electroencephalogram.
Specifically, an electroencephalogram interface is realized in which an electrode is worn on the parietal; words are randomly displayed on a screen; and a word which is selected by a user is determined by utilizing a positive component (P300 component) that appears in a time slot from 300 ms to 500 ms based on the timing of displaying the word which the user wishes to select as a starting point, for example.
In a conventional electroencephalogram measurement, electrodes are worn according to the position notation of the International 10-20 system, such that measurement is performed with a measurement electrode being worn on the parietal. In Patent Document 1, an electroencephalogram measurement is performed by using a characteristic signal at a Pz (median parietal) position or a Cz (median center) position according to the International 10-20 system. It is known that the characteristic signal utilized in Patent Document 1 is intensely measured at the location of the Pz position. Therefore, Pz is mainly used as an electrode position of conventional electroencephalogram interfaces.
The inventors have actually constructed an interface which determines an item that is selected by a user from among four options that are displayed on a TV screen by utilizing an electroencephalogram which is measured at the Pz position. In the following, any mention of an “electroencephalogram interface being constructed” will mean a similar interface being constructed.
An evaluation was performed for 8 test subjects, which revealed that determination was possible with a distinction ratio (a rate of correct results of determination within the total number of trials) of 81.3%.
However, an electroencephalogram measurement must be performed by using an electrode which is worn at the parietal as mentioned above. Therefore, in the case where a device which does not have a structure to come in contact with the parietal (e.g., the aforementioned HMD) is used, it is necessary to separately wear an electrode for measuring an electroencephalogram on the parietal. An HMD is a device which is not worn at all times but is worn only when necessary, and is frequently attached or detached. Therefore, it would be a burden on the user to separately wear any electrode other than the HMD. This circumstance is also true of any device other than HMDs that does not have a structure to come in contact with the parietal.
Studies of acquiring a biological signal of a user by using an HMD are under way. For example, Japanese Laid-Open Patent Publication No. 7-64709 discloses a method in which an electrode is provided at a position on the inside of an HMD where the electrode comes in contact with the face of a user; an electro-oculographic potential and an electromyogram are measured; and a direction of a line of sight is detected. Japanese Laid-Open Patent Publication No. 9-38037 discloses a method in which electrodes are attached at up, down, right, and left positions of an eye and an electro-oculographic potential is measured by measuring potential differences between them. All of these are studies of measuring a response of a facial muscle (electromyogram) or an eyeball motion (electro-oculographic potential).